Procedure

   mxvg_c ( Matrix times vector, general dimension ) 

   void mxvg_c ( const void   * m1,
                 const void   * v2,
                 SpiceInt       nr1,
                 SpiceInt       nc1r2,
                 void         * vout   )

Abstract

   Multiply a matrix and a vector of arbitrary size.

Required_Reading

   None.

Keywords

   MATRIX
   VECTOR

Brief_I/O

   VARIABLE  I/O  DESCRIPTION
   --------  ---  --------------------------------------------------
   m1         I   Left-hand matrix to be multiplied.
   v2         I   Right-hand vector to be multiplied.
   nr1        I   Row dimension of `m1' and length of `vout'.
   nc1r2      I   Column dimension of `m1' and length of `v2'.
   vout       O   Product vector m1*v2.

Detailed_Input

   m1          is a double precision matrix of arbitrary size which
               forms the left-hand matrix of the multiplication.

   v2          is a double precision vector on the right of the
               multiplication.

   nr1         is the row dimension of `m1' and length of `vout'.

   nc1r2       is the column dimension of `m1' and length of `v2'.

Detailed_Output

   vout        is the double precision vector which results from
               the multiplication

                  vout = (m1) x v2

               `vout' has length `nr1'.

               `vout' may overwrite `m1' or `v2'.

Parameters

   None.

Exceptions

   1)  If memory cannot be allocated to create the temporary matrix
       required for the execution of the routine, the error
       SPICE(MALLOCFAILED) is signaled.

Files

   None.

Particulars

   The code reflects precisely the following mathematical expression

   For each value of the subscript `i' from 1 to `nr1',

      vout(i) = Summation from k=1 to nc1r2 of  ( m1(i,k) * v2(k) )

Examples

   The numerical results shown for this example may differ across
   platforms. The results depend on the SPICE kernels used as
   input, the compiler and supporting libraries, and the machine
   specific arithmetic implementation.

   1) Given a 2x3 matrix and a 3-vector, multiply the matrix by
      the vector.


      Example code begins here.


      /.
         Program mxvg_ex1
      ./
      #include <stdio.h>
      #include "SpiceUsr.h"

      int main( )
      {

         /.
         Local variables.
         ./
         SpiceDouble          vout   [2];

         /.
         Define `m' and `vin'.
         ./
         SpiceDouble          m      [2][3] = { { 1.0, 1.0, 1.0 },
                                                { 2.0, 3.0, 4.0 } };

         SpiceDouble          vin    [3] = { 1.0, 2.0, 3.0 };

         /.
         Multiply `m' by `vin'.
         ./
         mxvg_c ( m, vin, 2, 3, vout );

         printf( "M times VIN:\n" );
         printf( "%10.3f %9.3f\n", vout[0], vout[1] );

         return ( 0 );
      }


      When this program was executed on a Mac/Intel/cc/64-bit
      platform, the output was:


      M times VIN:
           6.000    20.000

Restrictions

   1)  The user is responsible for checking the magnitudes of the
       elements of `m1' and `v2' so that a floating point overflow does
       not occur.

Literature_References

   None.

Author_and_Institution

   N.J. Bachman        (JPL)
   J. Diaz del Rio     (ODC Space)
   W.L. Taber          (JPL)

Version

   -CSPICE Version 1.2.0, 04-JUL-2021 (JDR)

       Changed input argument name "nrow1" to "nr1" for consistency with
       other routines.

       Updated short error message for consistency within CSPICE wrapper
       interface: MEMALLOCFAILED -> MALLOCFAILED.

       Edited the header to comply with NAIF standard. Added complete code
       example based on the existing example.

   -CSPICE Version 1.1.0, 25-JUL-2001 (NJB)

       Changed protoype: inputs "m1" and "v2" are now type
       (const void *). Implemented interface macro for casting inputs
       "m1" and "v2" to const.

   -CSPICE Version 1.0.1, 08-FEB-1998 (NJB)

       Corrected a comment describing the local macro INDEX. Made
       miscellaneous code format corrections.

   -CSPICE Version 1.0.0, 25-OCT-1997 (NJB) (WLT)

       Based on SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

Index_Entries

   matrix times n-dimensional vector

Link to routine mxvg_c source file mxvg_c.c